1. Field of the Invention
This invention relates to the retention of filter elements, principally in the art of vertically rotating disc filters, each composed of a plurality of filter segments.
2. Related Art
Examples of such filters are described in U.S. Pat. No. 3,283,906 to Crane and U.S. Pat. No. 3,331,512 to Vore. Each segment comprises a generally wedge shaped hollow plate with perforated surface webs, covered on each side with an appropriate filter cloth. Liquid is drawn into the cavities within the plate, through the filter cloths by suction achieved by known means, as the respective sector is dipped into an unfiltered slurry or other prefiltrate. Particles above the retention threshold of the filter cloths are retained by the filter cloths, whilst liquid and fine particles below the threshold pass into the interior of the segment plate, and are pumped therefrom. On emergence from the bath of unfiltered slurry, to be exposed to the air, the cake of retained particles on the filter cloth can be removed by scrapers or other known means.
Disc filters of this kind are commonly used in filtration of minerals such as coal dust, ores or the like. Each filter disc may comprise 8 to 12 sectors, each from 0.4 to 1.8 m in height, and two or three skilled workers may be needed to fit and remove each sector, which in known filters is required in order to remove old filter cloths, and fit replacements. A complete installation may comprise up to 200 filter wheels or more and the operation of changing filter cloths may take several days, as each sector may occupy 2-3 workers to remove, dress and re-fit so that each wheel may represent a full day""s work for each team employed.
An object of the invention is to provide means for retention of filter cloths on the segments of a disc filter, which will enable the filter cloths to be removed and replaced quickly and easily, and without removal of the segment from the wheel.
According to the invention, in a filtration apparatus, wherein the apparatus comprises two or more adjacent filtration sections, there is provided means for retaining at least one filter element over each filtration section, comprising an elongate member extending between adjacent filtration sections, said elongate member having respective grooves therein to receive an edge bead provided in each filter element.
Preferably the bead, or at least the lips of the grooves are of flexible material, to enable the bead to be pushed into and pulled from the grooves.
The filtration apparatus is preferably a vertical disc filter of the kind described above, but may be a horizontal pan filter, comprising a similar assembly of a plurality of segments, or a drum filter comprising a plurality of part cylindrical panels.
In the case of a disc filter, the elongate member may have a hollow core, to enable a sector dividing stem to pass along the elongate member. These stems provide mechanical strength to the structure of the disc.
In a preferred embodiment, the elongate member comprises an extrusion of profiled cross section of a hard plastics material, such as polypropylene, polyethylene or polyamide or a blend of two or more thereof, or of a lightweight metal such as aluminium or an alloy thereof. Two grooves may be provided at each side of the member to receive the edges of two filter cloths, one on each face, of each of the sectors abutting the elongate member.
The bead on each filter cloth edge is preferably an elastomeric extrusion, of e.g. natural or synthetic rubber or the like, which can be deformed to be forced into the respective groove, or to be pulled out from it. The bead may be formed with flaps or rods between which an edge of a filter cloth may be received, and secured for example by at least one of stitching or welding. It is noted that the bead is preferably made of a softer material than the elongate member.
The grooves of the elongate member are preferably circular in cross section, set deeper than their radius, so that they present an orifice slit which is less than the diameter of the groove, thereby forcing compression of the bead for insertion or withdrawal, and acting to retain the bead in normal use.
The invention also provides filtration apparatus comprising two or more adjacent filtration sections. Each section being provided with one or more filter elements, and retaining means for retaining the filter elements. The retaining means comprising an elongate member extending between adjacent filtration sections. The elongate member having a respective groove therein for receiving an edge bead provided on each filter element.